The German invasion of France via Belgium was slowed by spirited Belgian resistance and Russia's swift entry into the field, resulting in stalemate and trench warfare.

Neutral Rights and Submarine Warfare.The United States was provoked into entering the war when its neutrality was violated by German submarine attacks on its nonmilitary ships and foreign vessels on which Americans were passengers.

New Forms of Warfare.

Preparedness.

The Home Front.

The Peace Process. The Paris Peace Conference convened in January 1919 and eventually 32 nations, including the United States, attended  Germany was not among them. The chief result was the Treaty of Versailles.

The Treaties.The war was concluded by five treaties between the Allied victors and the individual defeated nations of the Central Powers. The Allies chose to reward those groups that had supported them and punish those who had opposed them.

Defeat in the Senate.The U.S. Senate failed to ratify the Treaty of Versailles, which contained President Woodrow Wilson's cherished League of Nations proposal. Therefore, the United States did not join the League.